It isn't a second router you need, it's a hub or managed switch, the WRT54GS might be configurable to do that if you can disable DHCP and maybe NAT in its menu. Whatever you do, never have more than one DHCP controller active on the same network or you will likely lose control of them all from any connected computer.
If it helps as an example, the configuration I use here is like this:
Satellite + 4G USB stick on mobile network + ADSL -------------> Draytek Modem/Router with DHCP enabled (it has multiple internet ports)
Draytek has 6 local Ethernet ports, LAN 1 - 5 go directly to networked devices,
LAN 6 goes to a Netgear 16 port hub with 13 directly connected network devices.
LAN port 14 on the Netgear hub goes to a Netgear DG834 router used only as a remote wireless access point,
LAN port 15 on the Netgear hub goes to a Netgear DGN2200 router used as a remote wireless access point and NAS port for backup storage
LAN port 16 goes to yet another Netgear 8 port hub which in turn feeds printers and an oscilloscope.
Only the Draytek router has DHCP enabled and the other two Netgear routers have it disabled and in any case have fixed IP addresses. It is a fairly complicated network but it covers three buildings with wired and wireless connections, has internet fallback if one source fails and gives me a backup facility in a remote building in case of disk failure on the main systems. All the wireless points have access control enabled so only authorized devices can connect to the network to keep it secure.
Brian.